|MadSci Network: Chemistry|
Chemical reactions occur because of the complex thermodynamic free-energy change. If the change in free energy by reactants, even one chemical with water, is negative, then the reaction can make energy available. If the change in free energy is positive than the reaction can occur only when an external energy source is available. When free energy is zero, the system is at equilibrium and no spontaneous change is possible. A boulder going down a hill, the change in free energy would be negative and, energy would be made available. Reactions in the body are influenced by catalysts (enzymes), body temperature, and acidity (stomach vs. other tissues as liver, etc.) Water is always necessary in body reactions.
Calories are determined in a bomb calorimeter that measures the energy (Calories) by measuring the heat produced by one gram of the material. The metabolic (usable) energy: carbohydrates: 4 Cal/g., lipids: 9 Cal/g, protein: 4 Cal/g.
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